In recent years there have been increasingly used endoscopes with driving wires for diagnosis of, e.g., the large intestine. And efforts have also been exerted in developing active catheters in which a shape memory alloy (hereinafter also referred to SMA) that is deformable when electrically heated is utilized to make up an actuator.
Further, with the progress of micro-machining technologies, efforts have been made to develop varieties of micro-sensors and active micromechanisms that may effectively be incorporated into catheters for medical applications.
For example, Japanese patent application No. H10-11258 filed Jan. 23, 1998 by the inventor of this application (JP Laid-Open publication No. H11-48171 published Feb. 23, 1999 proposes an active catheter of an outer skeleton type in which a liner coil is disposed outside of a plurality of, e.g., three, actuators which are made of a shape memory alloy. The SMA made actuators are electrically energized to permit the active catheter to be bent or flexed.
As to an extending and retracting mechanism for active catheters, there has been proposed an intra-tubular traveling apparatus having a tubular diameter of around 1 cm utilizing the inflation and contraction of a balloon under an atmospheric pressure, with which have been made on an experimental basis an endoscope guidance system for large intestines and a pipe orifice inspection guidance systems for town gas conduits (see “The World of Micro-mechanisms” by T. Hayashi et al, Journal of the Japan Society of Acoustics, Vol. 49, No. 8, 1993).
An extending and retracting mechanism having a number of balloons disposed on its side surfaces has also been proposed. This is designed to permit the catheter to be advanced in a blood vessel as the inflation of the balloons pushes them against the inner wall of the blood vessel and their contraction and expansion in its axial direction are repeated (see “Potential of microsystems in medicine”, Minimally Invasive Therapy & Applied Technology, 4: 267–275, 1995, A. E. Guver et al).
Active slender tubes so far proposed, such as those catheters or the like described above have not yet been sufficient, however, in their bendability and extendibility achievable, nor have they been wide enough in their degrees of freedom of movement selectable. Furthermore, if a single catheter is sought to have many more functions, its limited diameter and the need for a sufficiently spacious working channel in it have restricted the number of wires that could be incorporated to an insufficient extent.
It should also be noted that in orienting a manually operated catheter or guide wire that is normally bent towards its distal end in the form of the letter “J” so as to allow it to enter, e.g., into one of two blood vessels at their junction, it has been common practice to attempt to rotate the catheter or guide wire at its proximal end or side in order to rotate it at that distal end. Then, if the catheter or guide wire has in its midway a loop or an intricate travel or span, the torque to act to transmit the rotation at the proximal end to the distal end may fail to be well transmitted through the body of the catheter or guide wire, resulting in an insufficient manner, thus an inaccurate rotation of the catheter or guide wire at the distal or its foremost end will occur. This may be called a poor torquability.
Further, when the catheter or guide wire is pushed at its proximal end in order to advance its distal end towards a target position in a blood vessel, if the catheter or guide wire has a loop or an intricate travel or span a deflection that would then occur in the body of the catheter or guide wire would tend to prevent the pushing force applied at the proximal end from being accurately transmitted to the distal end, thus resulting in an imprecise positioning of the catheter or guide wire at its foremost end. This may be called poor pushability.
On the other hand, positioning the catheter or guide wire by retraction can be achieved relatively accurately. However, this operation requires the catheter or guide wire to be first advanced beyond the target position. Stiffening the catheter or guide wire improves its pushability and torquability, but increases the risk of perforation. Conversely, if the stiffness is reduced too much, deflection would prevent the catheter or guide wire from advancing any further however hard it may be pushed.